1. Technical Field
The present invention relates to a common mode filter and a method for manufacturing the same.
2. Description of the Related Art
Due to recent developed system configuration and increased data capacity, a high transmission rate is required, and for this high transmission rate, a differential signal type of transmission is mainly used.
Conventionally, if the signal frequency is increased in order to increase the transmission rate, undesired electromagnetic waves (i.e., noise) are generated due to high frequency of a signal, and the signal and the noise may overlap each other.
Hence, common mode noise is generated due to imbalance between high-rate differential signal lines (i.e., two signal lines).
A common mode filter is mainly used in order to remove this common mode noise. The common mode filter is an EMI filter mainly applied to the high-rate differential signal line.
This common mode filter contributes to improving in EMC characteristics of electronic devices and the like or improving antenna characteristics of cellular phones and the like.
In this common mode filter, a first coil and a second coil formed above the first coil are formed in a vortex shape, and an insulator sheet is formed between the first coil and the second coil.
When a common mode of noise is applied to the first coil and the second coil of the common mode filter of the prior art, impedance values of the respective coils are increased, and thus, the common mode of noise is removed.
However, in the common mode filter of the prior art, build-up layers need to be formed seven times or more, which causes high process costs and decreased yield due to the many processes.
Furthermore, the common mode filter according to the prior art has a track shape, which is unfavorable in reducing the size thereof due to a wide two-dimensional structure.